1. Field of the Invention
This invention relates generally to transimpedance amplifiers (TIAs) and, in particular, to a circuit arrangement having a transimpedance amplifier (TIA) connected to a current limiter circuit for limiting current to the TIA during an overdrive condition.
2. Description of the Related Art
A current to voltage converter or transimpedance amplifer (TIA) is used with a current source to condition or change a current signal to allow further processing of the current signal. Typically, photons are converted to current using a photomultiplier tube or photodiode and the current is then converted to a voltage in the TIA. The gain of the TIA is proportional to its feedback resistor and is subject to overdrive when the current signal exceeds a set limit. When an overdrive condition occurs, the TIA enters a non-linear saturated condition that requires time to recover and return to the linear mode of operation.
Overdrive conditions in a TIA generally occur when cosmic rays strike a scintillator or from Fresnel reflections in optical time domain reflectometry. The overdrive signals can be on the order of 60 dB or a factor of 1000 times greater than the normal signal of interest.
Prior art TIA circuit arrangements limit the current the TIA is forced to respond to during an overdrive condition by feeding back a TIA output signal to an input terminal of the TIA to provide clamping. Nonetheless, by feeding back a TIA output signal to an input terminal of the TIA, the TLA generally still enters the non-linear saturated condition. This operational condition can cause, especially in a monolithic integrated circuit, the generation of a thermal tail. A thermal tail is defined as the time required for a TIA operating in a non-linear saturated condition to recover and return to the linear mode of operation. The generation of the thermal tail slows down the operation of the TIA and can also lead to a loss of data in memory circuits.
Therefore, it is an aspect of the invention to provide a circuit arrangement for limiting the magnitude of the current the TIA is forced to respond to during an overdrive condition. Further, it is another aspect of the invention to prevent high output currents and non-linear operation of a TIA during an overdrive condition. The latter will prevent the generation of thermal tails during the operation of a TIA.